High Metallicity of the X-Ray Gas up to the Virial Radius of a Binary Cluster of Galaxies: Evidence of Galactic Superwinds at High-Redshift

TL;DR

This study measures the metallicity of the intracluster medium up to the virial radius of a binary galaxy cluster, providing evidence that powerful galactic superwinds at high redshift enriched the gas before cluster formation.

Contribution

First measurement of ICM metallicity up to the virial radius in a binary cluster, indicating pre-cluster enrichment by galactic superwinds rather than ongoing processes.

Findings

Metallicity is uniform (~0.2 Zsun) up to the virial radius.

High metallicity unlikely due to cluster collision or ram-pressure stripping.

Supports early enrichment of the proto-cluster region by superwinds.

Abstract

We present an analysis of a Suzaku observation of the link region between the galaxy clusters A399 and A401. We obtained the metallicity of the intracluster medium (ICM) up to the cluster virial radii for the first time. We determine the metallicity where the virial radii of the two clusters cross each other (~2 Mpc away from their centers) and found that it is comparable to that in their inner regions (~0.2 Zsun). It is unlikely that the uniformity of metallicity up to the virial radii is due to mixing caused by a cluster collision. Since the ram-pressure is too small to strip the interstellar medium of galaxies around the virial radius of a cluster, the fairly high metallicity that we found there indicates that the metals in the ICM are not transported from member galaxies by ram-pressure stripping. Instead, the uniformity suggests that the proto-cluster region was extensively polluted with metals by extremely powerful outflows (superwinds) from galaxies before the clusters formed. We also searched for the oxygen emission from the warm--hot intergalactic medium in that region and obtained a strict upper limit of the hydrogen density (nH<4.1x10^-5 cm^-3).